Patent Literature 1 cited below discloses a Global Positioning System (GPS) watch which adjusts time based on a satellite signal from a GPS satellite. This watch determines whether the watch is indoors or outdoors by determining whether the amount of electricity generated by a solar panel exceeds a threshold, or whether the output amplitude of an acceleration sensor exceeds a threshold. The watch executes a satellite signal receiving operation only when determining that the watch is outdoors, in an attempt to reduce electric power consumption. The watch adjusts time based on a time of week (TOW) that is contained in a satellite signal. The time of week TOW indicates seconds elapsed since 0 o'clock last Sunday.